Light irradiation methods advantages

Several solid-state photochemical reactions have been investigated with polycrystalline samples suspended in solvents. Solvents such as water, where the reactant and the product are likely to be insoluble, are usually chosen and a surfactant is added to maintain the suspension. There are at least two apparent advantages to this method. First of all, photochemical equipment commonly used for fluid samples can be readily adopted to solid-state reactions. Secondly, it is expected that all microcrystals in a powdered sample will be homogeneously exposed to the incident light in a well-stirred reactor. Interestingly, while several examples of solid-to-solid reactions in suspended crystals have been documented, there are some cases where the solvent is incorporated into the phase of the final product. In a report by Nakanishi et al. [134] it was shown that p-formyl cinnamic acid (51, Scheme 33) forms mirror-symmetric dimers. While irradiation of crystals suspended in hexane gave amorphous cyclobutanes in 85% yield, suspension of the crystals in water gave a 100% yield of a crystalline photodimer with one water molecule of crystallization. 

In chemical vapor deposition (CVD) reactive vapor precursors react to produce solid materials in the gas phase or at the solid-gas interface on the substrate surface at appropriate temperatures. Typical precursors used in the CVD process are metal hydrides, metal chlorides, and metal organic compounds. In the case that the precursor species are metal organic compounds, the process is called metal-organic chemical vapor deposition (MOCVD). The precursor molecules are introduced into a reactor sometimes with a carrier gas and decompose by means of heat, irradiation of UV light, or electrical plasma formed in the gas. Thermal CVD is the most commonly used method. This technique has an advantage that refractory materials can be vapour-deposited at relatively low temperatures,... 

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